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OPEN
Spatial control of chirality in supramolecular aggregates Maria A. Castriciano1, Denis Gentili1, Andrea Romeo1,2, Massimiliano Cavallini1 & Luigi Monsù Scolaro1,2
received: 16 November 2016 accepted: 26 January 2017 Published: 09 March 2017
Chirality is one of the most intriguing properties of matter related to a molecule’s lack of mirror symmetry. The transmission of chirality from the molecular level up to the macroscopic scale has major implications in life sciences but it is also relevant for many chemical applications ranging from catalysis to spintronic. These technological applications require an accurate control of morphology, homogeneity and chiral handedness of thin films and nanostructures. We demonstrate a simple approach to specifically transfer chirality to the model supramolecular system of J aggregates of the protonated form of tetrakis(4-sulfonatophenyl)-porphyrin by utilizing a soft lithography technique. This approach successfully allows the fabrication of an ordered distribution of sub-micrometric structures in precise and controllable positions with programmed chirality, providing a fundamental breakthrough toward the exploitation of chiral supramolecular aggregates in technological applications, such as sensors, non-linear optics and spintronic. Since the early resolution experiments in 1848 by Louis Pasteur and the later definition by Lord Kelvin in 18941, chirality has always been one of the hottest topics in chemistry and material science due to its manifold implication in life science, pharmaceutics and catalysis. Chirality occurs at the molecular level as enantiomers of an asymmetric carbon centred molecule and at the supramolecular level, on different length-scales2, from asymmetric structural arrangements, such as helices. In the last decades, chirality has been extended to applications in non-linear optics3 and more recently in spintronics4,5. These applications aim to combine the specific optical properties of chirality with the advantage of a supramolecular approach. However, their development is hindered by many problems, which appear transferring chiral systems from solution to solid state, since technological applications require accurate control of morphology, homogeneity and a controlled chiral handedness of thin films and nanostructures. To date, a strong effort has been focused on growing spatially uniform chiral films with a programmed handedness6, supramolecular structures7, in the artificial fabrication of chiral nanostructures8 and in patterning9,10. However, the local spatial control of handedness of chiral aggregates is not demonstrated and it is still a crucial open challenge. Here, we successfully address this problem in a model system, by using a straightforward procedure based on patterning, which combines deposition in confinement with the local induction of specific chirality imprinted by a chiral templating agent. In particular, we drive the self-assembly of a model porphyrin into chiral aggregates on a substrate by a wet lithographic method in which a polymeric stamp is functionalised by the two enantiomeric forms of an organic chiral acid, exploiting the so named “sergeants and soldiers effect”11 under lithographic control. J-aggregates of porphyrins are largely studied as model systems12–21 due to their peculiar optical properties; e.g., large extinction coefficients, resonant light scattering16, light harvesting17 and giant third-order optical nonlinearities12. Chirality in these systems adds the possibility of interaction with circular polarized light and their investigation by circular dichroism. Depending on the protocol for their preparation, porphyrin J-aggregates exhibit a large variety of morphologies, in which the molecular building blocks can self-organize into intrinsically chiral units13,14, giving racemates (i.e. mixtures of left-handed and right-handed chiral units) that can be easily biased through a variety of physical perturbations, such as vortex18, rotational and magnetic forces22, or using chemical chiral templates19. Kinetics of the assembling process control the eventual manifestation of chirality, both in bulk solution20 and in confined environments, such as in microemulsions20, or microfluidic conditions21.
1
Consiglio Nazionale delle Ricerche, Istituto per lo Studio dei Materiali Nanostrutturati, Italy. 2Dipartimento di Scienze Chimiche, Biologiche, Farmaceutiche ed Ambientali, University of Messina, and C.I.R.C.M.S.B., V.le F. Stagno D’Alcontres 31, Vill. S. Agata, 98166 Messina, Italy. Correspondence and requests for materials should be addressed to M.A.C. (email: [email protected]) or M.C. (email: [email protected]) Scientific Reports | 7:44094 | DOI: 10.1038/srep44094
1
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Figure 1. Scheme of the process. (a) A stamp pre-loaded with tartaric acid was placed over a film of 1 water solution spread onto the substrate. (b) On solvent evaporation, the solution stays pinned only to the protrusions, while the region in between the protrusions remains free of solution. During this stage, PDMS stamp releases the chiral agent (tartaric acid) due to osmotic effect. (c) When solution becomes supersaturated, aggregates form in the box shaped between the stamp protrusions.
We have proven our approach using tetrakis(4-sulfonatophenyl)-porphyrin (H2TPPS44−, (1)), which we consider as a representative for this class of nanoaggregates. The protonated green form of 1 (H4TPPS42−) self-organizes into J-aggregates13,14, whose formation can be easily detected by the large shift of the B-band to lower energy (
OPEN
Spatial control of chirality in supramolecular aggregates Maria A. Castriciano1, Denis Gentili1, Andrea Romeo1,2, Massimiliano Cavallini1 & Luigi Monsù Scolaro1,2
received: 16 November 2016 accepted: 26 January 2017 Published: 09 March 2017
Chirality is one of the most intriguing properties of matter related to a molecule’s lack of mirror symmetry. The transmission of chirality from the molecular level up to the macroscopic scale has major implications in life sciences but it is also relevant for many chemical applications ranging from catalysis to spintronic. These technological applications require an accurate control of morphology, homogeneity and chiral handedness of thin films and nanostructures. We demonstrate a simple approach to specifically transfer chirality to the model supramolecular system of J aggregates of the protonated form of tetrakis(4-sulfonatophenyl)-porphyrin by utilizing a soft lithography technique. This approach successfully allows the fabrication of an ordered distribution of sub-micrometric structures in precise and controllable positions with programmed chirality, providing a fundamental breakthrough toward the exploitation of chiral supramolecular aggregates in technological applications, such as sensors, non-linear optics and spintronic. Since the early resolution experiments in 1848 by Louis Pasteur and the later definition by Lord Kelvin in 18941, chirality has always been one of the hottest topics in chemistry and material science due to its manifold implication in life science, pharmaceutics and catalysis. Chirality occurs at the molecular level as enantiomers of an asymmetric carbon centred molecule and at the supramolecular level, on different length-scales2, from asymmetric structural arrangements, such as helices. In the last decades, chirality has been extended to applications in non-linear optics3 and more recently in spintronics4,5. These applications aim to combine the specific optical properties of chirality with the advantage of a supramolecular approach. However, their development is hindered by many problems, which appear transferring chiral systems from solution to solid state, since technological applications require accurate control of morphology, homogeneity and a controlled chiral handedness of thin films and nanostructures. To date, a strong effort has been focused on growing spatially uniform chiral films with a programmed handedness6, supramolecular structures7, in the artificial fabrication of chiral nanostructures8 and in patterning9,10. However, the local spatial control of handedness of chiral aggregates is not demonstrated and it is still a crucial open challenge. Here, we successfully address this problem in a model system, by using a straightforward procedure based on patterning, which combines deposition in confinement with the local induction of specific chirality imprinted by a chiral templating agent. In particular, we drive the self-assembly of a model porphyrin into chiral aggregates on a substrate by a wet lithographic method in which a polymeric stamp is functionalised by the two enantiomeric forms of an organic chiral acid, exploiting the so named “sergeants and soldiers effect”11 under lithographic control. J-aggregates of porphyrins are largely studied as model systems12–21 due to their peculiar optical properties; e.g., large extinction coefficients, resonant light scattering16, light harvesting17 and giant third-order optical nonlinearities12. Chirality in these systems adds the possibility of interaction with circular polarized light and their investigation by circular dichroism. Depending on the protocol for their preparation, porphyrin J-aggregates exhibit a large variety of morphologies, in which the molecular building blocks can self-organize into intrinsically chiral units13,14, giving racemates (i.e. mixtures of left-handed and right-handed chiral units) that can be easily biased through a variety of physical perturbations, such as vortex18, rotational and magnetic forces22, or using chemical chiral templates19. Kinetics of the assembling process control the eventual manifestation of chirality, both in bulk solution20 and in confined environments, such as in microemulsions20, or microfluidic conditions21.
1
Consiglio Nazionale delle Ricerche, Istituto per lo Studio dei Materiali Nanostrutturati, Italy. 2Dipartimento di Scienze Chimiche, Biologiche, Farmaceutiche ed Ambientali, University of Messina, and C.I.R.C.M.S.B., V.le F. Stagno D’Alcontres 31, Vill. S. Agata, 98166 Messina, Italy. Correspondence and requests for materials should be addressed to M.A.C. (email: [email protected]) or M.C. (email: [email protected]) Scientific Reports | 7:44094 | DOI: 10.1038/srep44094
1
www.nature.com/scientificreports/
Figure 1. Scheme of the process. (a) A stamp pre-loaded with tartaric acid was placed over a film of 1 water solution spread onto the substrate. (b) On solvent evaporation, the solution stays pinned only to the protrusions, while the region in between the protrusions remains free of solution. During this stage, PDMS stamp releases the chiral agent (tartaric acid) due to osmotic effect. (c) When solution becomes supersaturated, aggregates form in the box shaped between the stamp protrusions.
We have proven our approach using tetrakis(4-sulfonatophenyl)-porphyrin (H2TPPS44−, (1)), which we consider as a representative for this class of nanoaggregates. The protonated green form of 1 (H4TPPS42−) self-organizes into J-aggregates13,14, whose formation can be easily detected by the large shift of the B-band to lower energy (
